Yamamoto Seiichi, Toshito Toshiyuki, Komori Masataka, Morishita Yuki, Okumura Satoshi, Yamaguchi Mitsutaka, Saito Yuichi, Kawachi Naoki, Fujimaki Shu
Department of Radiological and Medical Laboratory Sciences, Nagoya University Graduate School of Medicine, 1-1-20 Daiko-Minami, Higashi-Ku, Nagoya, 461-8673, Japan,
Ann Nucl Med. 2015 Apr;29(3):268-75. doi: 10.1007/s12149-014-0936-4. Epub 2014 Dec 5.
In proton therapy, imaging of proton-induced positrons is a useful method to monitor the proton beam distribution after therapy. Usually, a positron emission tomography (PET) system installed in or near the proton beam treatment room is used for this purpose. However, a PET system is sometimes too large and expensive for this purpose. We developed a small field-of-view (FOV) gamma camera for high-energy gamma photons and used it for monitoring the proton-induced positron distribution.
The gamma camera used 0.85 mm × 0.85 mm × 10 mm Ce:Gd3Al2Ga3O12 (GAGG) pixels arranged in 20 × 20 matrix to form a scintillator block, which was optically coupled to a 1-inch-square position-sensitive photomultiplier tube (PSPMT). The GAGG detector was encased in a 20-mm thick container and a pinhole collimator was mounted on its front. The gamma camera was set 1.2 m from the 35 cm × 35 cm × 5 cm plastic phantom in the proton therapy treatment room, and proton beams were irradiated to the phantom with two proton energies.
The gamma camera had spatial resolution of ~6.7 cm and sensitivity of 3.2 × 10(-7) at 1 m from the collimator surface. For both proton energies, positron distribution in the phantom could be imaged by the gamma camera with 10-min acquisition. The lengths of the range of protons measured from the images were almost identical to the simulation results.
These results indicate that the developed high-energy gamma camera is useful for imaging positron distributions in proton therapy.
在质子治疗中，对质子诱导正电子进行成像，是监测治疗后质子束分布的一种有用方法。通常，为此目的会使用安装在质子束治疗室内部或附近的正电子发射断层扫描（PET）系统。然而，PET系统有时对于此目的而言体积过大且成本过高。我们开发了一种用于高能伽马光子的小视野（FOV）伽马相机，并将其用于监测质子诱导的正电子分布。
该伽马相机使用0.85毫米×0.85毫米×10毫米的铈掺杂钆镓石榴石（Ce:Gd3Al2Ga3O12，GAGG）像素，排列成20×20矩阵以形成一个闪烁体块，该闪烁体块与一个1平方英寸的位置灵敏光电倍增管（PSPMT）进行光学耦合。GAGG探测器被封装在一个20毫米厚的容器中，并且在其前端安装了一个针孔准直器。伽马相机被设置在质子治疗室中距离35厘米×35厘米×5厘米塑料模体1.2米处，并用两种质子能量对模体进行质子束照射。
该伽马相机在距准直器表面1米处的空间分辨率约为6.7厘米，灵敏度为3.2×10⁻⁷。对于两种质子能量，通过10分钟的采集，伽马相机能够对模体中的正电子分布进行成像。从图像中测量得到的质子射程长度与模拟结果几乎相同。
这些结果表明，所开发的高能伽马相机可用于质子治疗中正电子分布的成像。
